A conventional muographic observation instrument (MOI) takes the form of a number of orthogonally arranged muon counters. Each muon counter includes photomultipliers attached to the longitudinal edge of the square columned scintillator bar (for example, see JP 2013-156099). When a muon passes through the counter, photons are generated inside the scintillator, which are eventually converted to electrons by the photomultipliers and further amplified to an output signal with large amplitude. Depending on the position of the muon counter outputting the signal, the position of the incident muon can be identified in the muon counter, which is further used to identify the direction of the incident muon as well in the two-scintillator configuration.